I'm a non-native English speaker, and my automatic spellchecker seems to accept both therefore and therefor. Is one orthography preferred ? Is that a British vs. American difference ? Or an old vs. more recent orthography ? Or something else ?
Therefor means for that.
Here we sell guitars and accessories therefor.
Therefor is one of a whole series of adverbs: thereof (of that), thereafter(after that), therein (in there), etc.
If you are familiar with German - the Germanic sister of English - you can find a direct analogy there:
for = für
therefor, for that = dafür (literally, therefor)
Therefore, as you must know, means as a (logical) consequence
Therefore and therefor are completely different words.
Therefor, an archaic word, means "for this", "for that", or "for it". E.g;
... ordering goods and enclosing payment therefor.
Therefore means "for that reason" or "hence".E.g;
Those people have their umbrellas up: therefore, it must be raining